The government's announcement that it will make fully available all documents relating to the Hillsborough disaster, and that ministers have agreed how that process will happen, is a huge achievement for the Hillsborough Family Support Group.

Ordinary people who lost their loved ones in horrific circumstances at a showpiece football match in 1989, the families are recognised now to have fought a noble campaign, for 20 years, for the full truth to be revealed about the disaster, and what happened afterwards.

On the 20th anniversary this year, the families finally experienced a watershed in the public's attitude to the disaster, with sympathy flowing overwhelmingly behind them. Andy Burnham, then the culture secretary, now health minister, with Maria Eagle, the junior justice minister, made the call for all documents to be released after reading the Guardian's coverage, which reported the families' enduring complaints that unanswered questions still remain.

That was before Burnham attended the memorial service at Anfield on April 15. The chanting which interrupted his speech on the day was a difficult moment for him, but it powerfully drew the government's attention to the strength of feeling which persists about Hillsborough. At Tuesday's meeting, attended by Burnham, Merseyside MP Derek Twigg and Justice Minister Michael Wills, the Home Secretary, Alan Johnson, agreed that all documents will be disclosed, although the families will be able to see sensitive material relating to their loved ones before the documents are made fully public. An independent panel will be appointed to the huge task of sifting and scrutinising the documents, and based on all that information, will produce their own account of what happened.

The families, represented by the group's chair Margaret Aspinall, vice-chair Pat Joynes, president Trevor Hicks and sub-committee member Jenni Hicks, all of whom lost children in the disaster, asked that professor Phil Scraton, author of Hillsborough: The Truth, should be their representative on the panel. Aspinall told me they wanted Scraton, who has carried out a sustained critical analysis of the disaster, to be the panel's chairman, and able to appoint two more of its members.

She explained that the families are still cautious, because they have felt crushingly let down by the legal system in the past, but do recognise they have secured an achievement by coming this far.

"We are bereaved families who have had to fight for 20 years," she said. "All we have ever wanted is the full truth about what happened and for those at fault to accept responsibility. This is progress, certainly, and we feel some trust in Alan Johnson and the government this time, but we will not be satisfied until a thorough job has been done examining all the documents disclosed."

Meredydd Hughes, the chief constable of South Yorkshire Police, told the Guardian before the 20th anniversary that he was committed to openness and would "trigger a review" to see what documents the force still had. Hughes said then that he believed the ten boxes the force had deposited in the Parliamentary library years ago were the full archive – but it has turned out the police have 500 further boxes in their archives; an estimated 500,000 documents in total.

Cataloguing that mountain of material is expected to take "many months," according to police sources, and the other public bodies, including the ambulance service, fire brigade and Sheffield City Council, will need time to assemble theirs, too. Permission will be required from the South Yorkshire coroner's office to have documents released, because, in law, coroners' documents normally remain confidential for 70 years. The consent of the Conservative Party will be necessary if government documents relating to the disaster are to be released, because the Tories were in power at the time. As Sheffield Wednesday Football Club is not a public body, it will not be covered by the Home Office commitment and so the club will have to consent separately if it is to release its own files.

This is, then, a landmark moment, but there is still a long way to go before the Hillsborough families will discover, after more than 20 years, the full truth about what happened to their loved ones, and how those responsible for their safety behaved in the disaster's aftermath.